Dual frequency antenna



Patented Aug. 16, 1949 Tino :niesne This riiwentiim.rellates-togaitennas f for cornninnioationystenis.andgrnorleparticularly to an antenna .ip r. use as lag Juie'aeo-nfin.connection with rad-iofobect-.locating Ls'ysten- 1`s sirable @tol:utilize ,a frendxor .."foe -interrogation (IEE) kWit/tia :tangetseachtindication. I tlisialso desired toobtain 5511.10'si'antiallyuniform omnidirectional radiation;o ff-.eisierg'y- I-Ieretoiore, itfh'asbeeneconsidered :rieqelssarynthair beacon antenna for-fobtainingnnifornieoninidirectional radiation be^radial1ly symrnetricaii incrosslesedtionand' that separate-,antennas the :used as ea beacon and.'f or EFF-interrogation. n

itfhasfnowebeenifminid thatfsiibstantially Luni; formtomnidirectionadiationimayabepbtained with'-an ant enna fa s'yrnmetrica1 `incrosss'eotion such esfof streamlined tearedropior evene-'recetang/ula'rcross-secton- `Such anqantenna .has

beencdiselosed -in thefcopending application of Henry -J.Rib1e1;,seria1=Nn, f62ri,o4o,.LmedgNovember :6, V19415, 'entitled .?Antenna.,'Ihisrinvention contempates van #improgeitnenteof the ,inventionof"themforesaiducopendin pplcationfandfom'- bines therewith meansfor:sinniltaneoslymadiatingfenergy.ofitwo difierentreguencies`T'Ihusfmzler of .thefcbectsiof'thejpres'entinventionl'is fto utilizeahsingle =antenna :adapted Vto transmit and receive energy at @two.different ranges offrequencies .fsininltaneoslesuch asa f' microwave:frequeney range @having wavelengths of the order ofcentimetelgsforvguse as aheacon inconnection,withragiiogobject-locatingsystems, arid asionger wave :frequency grangeliaving Wavelengths s ofthe AVordereef,metersorlonger for the i .It iswanotherobjeetoffftheinyention .to provide .a beacon antenna having a streamlined,,teandrop ,or other non-,circular f shape Lin V.Ygross-:section capable.o radiating energypt twodierent ranges ,of frequencies finsubstantially -uniiorm Aomnidirectional radiationpatterns.:

Forsa better understar-nii n g,oi. tI-1 e Airwentionltogether with'other -and further bjects thereof,

'reference is :had to, thefollowingdescriptmn f'- rlgfflfisaalongitudinal sideiiseetional viewof the antenna'according Ttof-thepresent invention;

E'Figxfs; isf'a transversegseotional vieweofttheean- 'tenna of Figs. 1fand l2itakenAsiibstari-ti ally .,along zthe;1ine-:3.0f=Fi g.r2; f f

incliidingfpipe l`| 1entend' the4 approximate ent 3 coming the othersection of a dipole radiator. Energy is fed to the long wave dipoleradiating element 2'I comprising sections I3 and I 4 by means of acoaxial conductor transmission line 28 connected to a source of lowerfrequency energy not shown. The center conductor 29 of coaxial line 28extends beyond the end of the outer conductor 30 and is connected to theupper dipole section I3, for example, through a transverse partitionmember 3| connected -to the wall o f dipole section I3. The outerconductor 30 is connected to the lower pipe or dipole section I4 bymeans of a transverse partition member 32. It will thus be understoodthat the pipe or dipole sections I3y and I4 comprising the long Waveradiating element 21 is excited by means of the coaxial line 28 and isadapted to radiate energy of longer wave lengths than, or of lowerfrequencies than, that of the microwave energy. Also such longer waveenergy is radiated in a substantially uniform omnidirectional pattern.-With the antenna in its contemplated vertical position, radiations ofboth frequencies will therefore have approximately uniform azimuthpatterns.

In order to prevent any lower frequency excitation from interfering withthe high frequency transmission through antenna IIJ, and particularly tokeep the low frequency or long wave signais from being carried along theoutside surface of line 2| inside of the aircraft, the long wave dipole21 is shortedby a stub 33. Stub 33 comprises the inner surfaces ofpartition 32, and of lower pipe section |4' which is shorted at thejunction of antenna IIJ with the base I2 by means of a plate 34, theinner conductor of the stub 33 being the outer surface of coaxial line2| extending longitudinally therethrough. Inasmuch as the outerconductor I4' of this stub is large compared with the outer surface ofthe coaxial line 2l, the characteristic impedance of the stub 33 will belarge Yand the admittance will be reasonably small even though thelength X of the stub 33 is only, for example, of the order of V3wavelength of the longer wave energy. The overall'length of-antenna I 0and the length of the bottom pipe or dipole section I4 are so chosen asto obtain proper-impedance matching for the long wave dipole radiatingelement 21 comprising the sections I3 and I4. It has beeen found thateven though the currents ofboth the higher and lower frequency ranges ofenergy both exist on the upper section V|3, the polarization is suchthat no interference exists between energy of one frequency with that ofthe other and that radiation of both frequency ranges can simultaneouslybe emitted from antenna I l) without interference.

With the arrangement as. described hereinbefore, theantenna has severaladvantages over known types of beacon antennas. In `the first placebecausethe microwave radiating element comprises slots rather thanVdipoles and because of the streamlined nature of the entire assembly, atight fitting housing may be used which may be small and streamlined forlow wind drag effect. Also, since the microwave frequency antenna ismounted at the upper end of the longer wave radiating element ratherthan in the bottom section, the nulls in the elevation pattern Ydue toreflections from the skin surface of the aircraft are less likely tooccur and are less serious than would otherwise occur. Also, the antennaas thus described provides a more compact, light-weight easilyconstructedand easily mountable structure than heretofore known. Y e

While there has beendescribed what is at pres- 4 ent considered thepreferred embodiment of the invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention.

What is claimed is: l 1. An antenna for radiating electromagnetic energyof two different ranges of frequencies,

l comprising a hollow pipe of electrically conductive material and ofstreamlined shape in crosssection, said pipe comprising two aligned pipesections forming upper and lower pipe sections when said pipe is in' itscontemplated vertical position, a ring of dielectric material separatingsaid upper and lower sections, whereby said sections comprise the twopoles of a dipole radiating element, a coaxial transmission linedisposed within said pipe and longitudinally thereof adapted to transmitenergy of one range of frequencies, means for coupling said coaxial lineto each of said pipe sections whereby said sections are adapted to beexcited by and to radiate said energy, the walls of said upper pipesections on opposite sides of the major axis of the crosssection thereofeach having a slot disposed longitudinally of said upper section andalong the approximate centerline of each of said walls whereby saidslots are directly opposite each other, said upper pipe sectionincluding said slots comprising a second radiating element adapted toradiate energy of a different range of frequencies than said dipoleradiatingV element, and means for feeding energy of said diiferentrange'of frequencies `to and for exciting said second radiating element, saidmeans including a second coaxial line extending longitudinally throughsaid hollow pipe, and means for coupling said Vsecond c0- axial line tothe edge portions of said slots, said dipole radiating element andsecond radiating element being adapted to be excited by and to radiateenergy of both said ranges of frequencies simultaneously withoutinterference of one with the other in substantially uniformomnidirectional radiation patterns in planes perpendicular to said pipesections.

2. An antenna as claimed in claim 1 wherein said second radiatingelement is adapted to be excited and to radiate energy within themicrowave range of frequencies and said dipole radiating element isvadapted to be excited by and to radiate energy within a range of lowerfrequencies than said microwave energy.

3. An antenna as claimed in claim 1 wherein means are provided forshorting said lower pipe section at the base thereof whereby said lowerpipe section forms a stubY to prevent energy currents being carried onthe outer surface of said second coaxial line.

4. An antenna as claimed in claim 1 wherein the outer conductor of' saidfirst-mentioned c0- axial line extends upwardly substantially to theupper end of said' lower section and the inner conductor'thereof extendsbeyond said outer conductor, said means for coupling said first coaxialline to said pipe sections comprising a member connecting said outerconductor'to said lower section and a member connecting said innerconductor to said upper section, and wherein said means for couplingsaid second coaxial line to said slots comprises a balanced dipoletermination of said secondrcoaxial line, one element of said dipoletermination connecting the inner conductor of Ysaid second coaxial lineto the midpoint of the edge portion of onev'of said. slots, the otherelement of said dipole termination connecting the outer conductor ofsaid second coaxial line to the midpoint of the edge portion of theopposite slot, said coaxial lines being disposed substantially parallelto each other within said pipe.

5. An antenna for radiating electromagnetic energy of two differentranges of frequencies simultaneously in substantially uniformoninidirectional radiation patterns in planes perpendicular to the axisof said antenna comprising a substantially hollow pip-e of electricallyconductive material and of non-circular cross-section, said pipecomprising two aligned pipe sections affording upper and lower pipesections when said pipe is in its contemplated vertical position, amember of dielectric material separating said sections whereby saidsections form the two poles of a dipole radiating element, means fortransmitting energy of one range of frequencies to and energizing saidtwo poles, said upper section having at least one slot in each of twoopposed sides thereof said slots being disposed longitudi nally of saidupper section and means for feeding energy of a different range offrequencies to said slots whereby said upper section is adapted toradiate said last-mentioned energy.

6, An antenna for radiating electromagnetic energy of two diffe-rentranges of frequencies simultaneously in substantially uniformomnidirectional radiation patterns in planes perpendicular to the axisof the antenna comprising a substantially hollow pipe of electricallyconductive material and of non-circular cross-section, said pipecomprising two aligned pipe sections affording upper and lower pipesections when said pipe is in its contemplated vertical position, saidsections forming two poles of a dipole radiating element, means fortransmitting energy of one range of frequencies to and energizing saidtwo poles, said upper section having at least one slot in each of twoopposed sides thereof said slots being disposed longitudinally of saidupper section and means for feeding energy of a different range offrequencies to said slots whereby said upper section is adapted toradiate said last mentioned energy EDGAR N. GILBERT.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,251,997 Goldmann Aug. 12, 19412,287,220 Alford June 23, 1942 2,349,942 Dallenbach May 30, 19442,362,561 Katzin Nov. 14, 1944 2,398,096 Katzin Apr. 9, 1946 2,404,196Seeley July 16, 1946 Y2,414,266 Lindenblad Jan. 14, 1947 FOREIGN PATENTSNumber Country Date y 523,074 Great Britain July 4, 1940

